The present invention relates to a semiconductor device, and particularly to a semiconductor device having a capacitor of a large capacity and a high reliability which uses a high dielectric constant insulating film as the capacitor insulating film.
With an increasing integration density of an LSI (large scale integrated circuit), miniaturization of a capacitor as the constituent of the LSI has been increasingly demanded. Thus, it was attempted to use a tantalum oxide (Ta.sub.2 O.sub.5) having a relative permittivity of 22, which is more than 6 times as high as that of silicon dioxide (SiO.sub.2) used as a conventional capacitor insulating film, for the purpose of increasing the capacitance of the capacitor, whereby the size of a semiconductor device is reduced, as described in, for example, Japanese Pat. Laid-Open Nos. 61,634/1983 and 4,152/1984.
However, part of the above-mentioned Ta.sub.2 O.sub.5 is chemically reacted with an element contained in an upper electrode, for example, silicon (Si), during a heat treatment conducted in the course of MOSLSI production after formation of a capacitor to give Ta, whereby the dielectric strength of the capacitor is lowered. This reaction is expressed by the following formula (1): EQU 2Ta.sub.2 O.sub.5+ 5Si.fwdarw.4Ta+5SiO.sub.2 (1)
A polycrystalline Si film, which is most chemically stable during the course of production of a semiconductor device, is most widely used as the upper electrode of a capacitor. However, when a high dielectric constant insulating film such as the above-mentioned Ta.sub.2 O.sub.5 film, which is suitable for increasing the integration density of a semiconductor device, is used as a capacitor insulating film, Si of the polycrystalline Si film is diffused into the Ta.sub.2 O.sub.5 film and reacted with the Ta.sub.2 O.sub.5 film by the heat treatment in the course of production of the semiconductor device.
Accordingly, in the above-mentioned prior art technique, a high melting point metal or compounds thereof, such as a silicide, having a concentration of Si lower than the stoichiometric one must be used in the upper electrode in order to prevent the reaction of Si in the upper electrode with the Ta.sub.2 O.sub.5 film. However, the above-mentioned high-melting point metal or compounds thereof having a low Si concentration is so chemically unstable that it is readily oxidized by a heat treatment in the course of production or readily corroded by a chemical such as an etching solution.
Thus, a high dielectric constant insulating film is difficult to use in MOSLSI according to the prior art technique.
U.S. Pat. No. 4,151,607 discloses that the use of a Si.sub.3 N.sub.4 film or a Ta.sub.2 O.sub.5 film instead of a SiO.sub.2 film as the insulating film of a capacitor is effective in decreasing the required area. However, there is no description as to an increase in leakage current caused by the reaction of Ta.sub.2 O.sub.5 with silicon.